/**
 * @desc 图片操作
 * @author zjl
 * @date 2020/6/20
 */

export function compressByImg (fileObj) {
  try {
    return new Promise((resolve, reject) => {
      const image = new Image()
      image.src = window.URL.createObjectURL(fileObj)
      image.onload = function () {
        const that = this
        // 默认按比例压缩
        let w = that.width
        let h = that.height
        const scale = w / h
        w = fileObj.width || w
        h = fileObj.height || (w / scale)
        let quality = 0.3 // 默认图片质量为0.4,值越大质量越好,相对的压缩率也会降低
        // 生成canvas
        const canvas = document.createElement('canvas')
        const ctx = canvas.getContext('2d')
        // 创建属性节点
        const anw = document.createAttribute('width')
        anw.nodeValue = w
        const anh = document.createAttribute('height')
        anh.nodeValue = h
        canvas.setAttributeNode(anw)
        canvas.setAttributeNode(anh)
        ctx.drawImage(that, 0, 0, w, h)
        // 图像质量
        if (fileObj.quality && fileObj.quality <= 1 && fileObj.quality > 0) {
          quality = fileObj.quality
        }
        // quality值越小，所绘制出的图像越模糊
        const base64 = canvas.toDataURL('image/jpeg', quality)
        resolve(base64)
      }
    }).then(result => {
      return result
    })
  } catch (e) {
    console.log('压缩失败!')
  }
}
